Ms. Latham et al., THE IMPACT OF GE GRADING ON THE BIAS AND TEMPERATURE CHARACTERISTICS OF SIGE HBT PRECISION VOLTAGE REFERENCES, Journal de physique. IV, 6(C3), 1996, pp. 113-118
We analyze the effects that the Ge profile shape has upon the bias and
temperature characteristics of SiGe HBT's. The widely used bandgap re
ference (BGR) design equation and a more general analytical expression
we developed incorporating Ge grading are used to compare silicon dev
ices to their SiGe counterparts. Measurement and simulation show that
although the Ge-ramp effect is negligible in the -55 to 85 degrees C r
ange, it can become important as the temperature drops, perhaps affect
ing the operation of SiGe circuits in the 77 K regime.